This invention relates to a powder metallurgy process for forming steel articles. More particularly, this invention relates to a method for producing steel rods and wire using mill scale, iron ore, or taconite as the metallic iron source.
Large amounts of particulate waste in the form of scale is produced at steel-making facilities. The scale is a coating of oxide formed at high temperatures during rolling or forging operations. Thus, steel ingots, billets and other semifinished forms are reheated in furnaces and converted into shapes such as sheets, bars and structural forms in continuous rolling mills, which force hot oxidized particles, known as scale, from the billets or other shapes during the operation. Mill scale is largely particulate iron oxide. Previously, such material has been discarded, notwithstanding the large amounts of iron available for recycle. More recently, processes have been devised for placing the mill scale in a form which will permit recycle of the mill scale in the form of briquettes containing iron adapted for use as feedstock to steel-making furnaces. Such processes are described for example in U.S. Pat. No. 4,369,062 and U.S. Pat. No. 3,870,507.
Powder metallurgy processes have been used to produce steel articles for more than 45 years. For example, U.S. Pat. No. 2,152,006 to Welch discloses a process which compacts and shapes, in a mold, mixtures of metallic powders and binders under a pressure of the order of 2,000 pounds to the square inch and upward. The shaped and coherent body is then removed from the mold, packed in finely divided alundum or equivalent refractory material, within a suitable tube or boat of carbon or other refractory; and so packed, is placed into a sintering furnace. After sintering at 1500.degree.-2000.degree. F., the compacted mixture is shaped by forging, rolling, die-pressing or the like. The shaped article is then heated to a higher temperature just below the melting point of iron whereupon the component metal powders combine to form the intended alloy while retaining their shape. Upon cooling, a usefully shaped metal article is produced. Unfortunately, however, metal articles produced by the Welch process lack the density (and therefore the strength) of articles produced from conventional rolled steel formed from poured steel ingots.